Acrolein is a highly toxic and flammable material. It is conventionally produced by the vapor-phase oxidation of propylene over a solid-phase catalyst, producing a crude, gaseous reaction product which contains acrolein, water vapor, acrylic acid, acetaldehyde, and other organic by-products. Typically, the gas is treated to remove acrylic acid, then contacted with cooled water for absorption of the acrolein. The resultant aqueous solution is distilled to recover the absorbed acrolein and other organic components. The crude acrolein is then refined to reject lower-boiling impurities such as, for example, acetaldehyde, producing a purified, liquid acrolein product. Since the conventional processes typically use a batch reaction system, condensation and in-process storage of liquid acrolein is often necessary as a surge buffer between the acrolein production process and the process to produce derivatives of acrolein.
Storage of liquid acrolein involves significant toxicity, fire and explosion hazards. High capital and operating costs are consequently incurred in providing for the safe handling of acrolein. Substantial enhancements in the safety of handling acrolein would be achieved if acrolein were transferred directly and continuously from the acrolein manufacturing process to the acrolein derivative reaction zone without intermediate storage. Since the conventional, commercial processes for the preparation of acrolein derivatives, e.g., methylmercaptopropanal, also known in the art as 3- (methylthio)-propanal ("MMP") involve liquid-phase reactions, the need to condense the gaseous acrolein product has been considered unavoidable. However, further enhancements in the safety of handling acrolein and the process efficiency of manufacturing acrolein derivative could be achieved if the acrolein were transferred to the acrolein derivative reactor in the vapor phase, i.e., without significant condensation of the acrolein.